The present invention relates to electrical installations, and more particularly to electrical conduit fittings for hazardous locations. More particularly still, the present invention relates to a drain hole core for forming a drain hole in drain seal fitting to prevent the accumulation of water in an electrical conduit.
The electrical wiring extending from one portion of an electrical installation to another, passes through metal conduit to protect the electrical wiring. Fittings with seals are installed in the conduit to prevent the passage of gases, vapors or flames from one portion of the electrical installation to another through the conduit thereby limiting any explosion in the enclosure and preventing pre-compression or "pressure piling". The National Electrical Code requires that seals be installed in specific locations. While not a National Electrical Code requirement, many engineers consider it good practice to sectionalize long electrical conduit runs by inserting seals approximately 50 to 100 feet apart, depending upon the conduit size, to minimize the effects of "pressure piling". Breathers or vents, are installed in the top of the enclosure to provide ventilation to minimize condensation in the enclosure.
Conduit seals are not intended to prevent the passage of liquids, gases or vapors at a continuous pressure differential across the seal. Even at differences in pressure across the seal equivalent to a few inches of water, there may be a slow passage of gas or vapor through a seal and through the electrical conductors passing through the seal.
Various considerations are made in selecting an appropriate seal fitting. Initially, the seal must be appropriate for the particular hazardous vapor involved. Then, a sealing fitting is selected for proper use with respect to its mounting position in the conduit run. This is particularly critical when the conduit runs between hazardous and non-hazardous areas. If the seal fitting is improperly positioned, hazardous gases or vapors may enter the system beyond the seal and permit the hazardous gases or vapors to escape into another portion of the hazardous area or to enter a non-hazardous area. Some seal fittings are designed to be mounted in any position. Other seal fittings are restricted to vertical mounting.
The seals include a fiber and compound. The fiber is used to provide a dam inside the fitting while filling the fitting with compound while it is in its liquid state. The compound, when properly mixed and poured, hardens into a dense, strong mass which is insoluble in water, is not attacked by petroleum products, and is not softened by heat. It will withstand, with ample safety factor, pressure of the exploding trapped gases or vapor. Electrical conductors sealed in the compound should be of the approved thermoplastic or rubber insulated type.
In locations which are usually considered dry, surprising amounts of water frequently collect in the conduit systems. No conduit system is air tight, therefore, it may "breath". Alternate increases and decreases in temperature and/or in barometric pressure, due to weather changes or due to the nature of the process carried on at the location where the conduit is installed can result in condensation and water accumulation within the conduit. Outside air is drawn into the conduit system when it "breaths in". If this air carries sufficient moisture it will be condensed within the conduit when the temperature decreases and chills this air. The internal conditions being unfavorable to evaporation, the resultant water accumulation will remain and be added to by repetitions of the breathing cycle. In view of this likelihood, it is therefore good practice to ensure against such water accumulations and possible subsequent insulation failures by installing breathers, drain seals, or inspection seals.
Seal fittings with drains are installed in the conduits in humid atmospheres or in wet locations where it is likely that water can gain entrance to the interiors of the enclosures or conduits. The conduits typically are inclined so that water will not collect in the enclosures or on the seals, but will be led to low points in the conduit runs where the water may pass out through the drains. Frequently, however, the arrangement of conduit runs makes this method impractical if not impossible. Drain seal fittings allow the draining of the water to prevent harmful accumulations of water above the seal.
The prior art method of providing a drain hole through the sealing compound of an explosion-proof drain seal fitting includes the use of a combination of a soft wire, inserted in a rubber tube, and a fiber washer. The wire/tubing core is inserted through the fiber washer, which is then inserted into the drain opening of the fitting. Seal fittings of the trade, sizes one-half inch to three inches inclusive, have round threaded cover openings of ample size for the placing of fiber dams in the conduit hub.
The sealing compound has to be set for a period of time, usually a minimum of two hours, before the wire/tubing core is removed. The wire is first pulled out of the tubing, then the tubing is pulled out of the fitting, leaving a path through the sealing compound for drainage.
Often the washer, which provides a dam for the unset compound, is not positioned correctly and thereby allows the sealing compound to flow into and fill the threads where the drain seal fitting is to be installed.
If the wire/tubing core is not removed after the seal is poured, or if the protruding end is cut off as observed in some installations, it will impair the function of draining water from the conduit. The top of the tubing inside the seal normally extends above the top of the sealing compound. Water can accumulate on top of the seal until the height of the tubing is reached, before any draining can occur. The presence of the wire inside the tubing will block or greatly restrict water drainage.
Since it is possible to remove the core, or cut it off at the opening, it is difficult to inspect a drain seal to determine if it was installed correctly.